It is known that currents can be induced into such circuits due to, for example, lightning strikes, and crossing or contact, of low voltage lines with high voltage lines. Such induced currents can damage sensitive solid state components and accordingly must be protected against.
Presently, protection against sneak currents is typically provided by inserting a fuse element in at least one line and preferably both low voltage lines of the telephone or other equipment circuit. In some applications, the fuse provides primary protection and in other applications, the fuse is used in combination with other protection devices such as, for example, a gas tube and/or silicon avalanche suppressor type protectors which are primarily voltage protection devices. In that case, up to, for example, four fuses may be utilized.
In any case, present sneak current protectors suffer from a primary shortcoming in that they do not meet all proposed industry accepted standards for sneak current protectors and in particular those according to proposed Underwriters Laboratory tests UL1459 and UL497A. These proposed standards first require that the protection device function at up to 600 volts AC and up to 350 amperes. The also requires that the protector must function by opening the circuit at the designated voltage and current levels without the functioning of a standard fuse element provided within the test circuit. Furthermore, the protection device must function without conflagration, that is without risk of fire as also determined by certain specified objective test effects. As noted, there presently is no known sneak current protection device that complies with all proposed industry accepted standards and requirements.